Synthetic hydrocarbon based grease compositions

ABSTRACT

HYDROGENATED HIGH-NAPHTHENIC CONTENT OLIGOMERIZED ALPHA-OLEFIN LUBRICATING OIL THICKENED TO GREASE CONSISTENCY WITH CLAYS AND OTHER CONVENTIONAL GREASE THICKENERS.

United States Patent 3,712,864 SYNTHETIC HYDROCARBON BASED GREASE COMPOSITIONS Donald E. Loeffler, Ferguson, Mo., George D. Hussey, East Alton, Ill., and George Smith, Pinole, and Johannes M. Wortel, Walnut Creek, Calif., assignors to Shell Oil Company, New York, NY. No Drawing. Filed June 17, 1970, Ser. No. 47,125

Int. Cl. C10m 7/02, 7/14 US. Cl. 252-28 Claims ABSTRACT OF THE DISCLOSURE Hydrogenated high-naphthenic content oligomerized alpha-olefin lubricating oil thickened to grease consistency With clays and other conventional grease thickeners.

This invention relates to grease compositions having improved performance properties. More particularly, it relates to grease compositions containing as the oleaginous base vehicle an oligomerized alpha-olefin lubricating oil of unique molecular structure and composition.

Conventional lubricating greases prepared from petroleum lubricating oils or refined mineral oils generally do not perform satisfactorily in applications such as the lubrication of jet aircraft because of the environmental extremes to which such greases are subjected. Specialized greases are required for this function, normally employing as the base vehicle one or more synthetic lubricating oils, e.g., synthetic esters such as trimethylol propane esters, neopentyl and pentaerythritol esters, dibasic acid esters, silicate esters and the like.

While greases based on synthetic esters generally are more stable than mineral oil based greases, they have the disadvantages of being detrimental to sealants and as a rule have poorer lubricity properties than conventional greases.

Another class of specialized greases are those containing olefin polymers either as a base stock component or as the sole base vehicle. Typical fluids of this type include polypropylene, polybutene and higher olefin polymers, for example, fluids produced by polymerizing straight or branched chain olefins in the C range with catalysts such as boron trifluoride or diteritary alkyl peroxides. The resulting olefin polymer base fluids are generally parafiinic in nature, have relatively good high and low temperature properties and do not adversely effect sealants. While greases prepared from olefin polymers possess certain advantages over reconventional mineral oil or ester-based greases, even these improved compositions have inherent limitations which diminish their utility at extremely high or low temperatures. In order to provide adequate lubrication at high temperatures, ideally it is desirable that the base lubricating vehicle have a relatively large proportion of high molecular weight components to provide a sufliciently thick film to prevent excessive wear of bearing surfaces. The presence of such high molecular weight components, however, particularly, if they are paraffinic in nature, can adversely affect the low temperature properties of a grease because of the tendency of parafiins to solidify at very low temperatures. As a result of these competing factors, conventional polyolefin-based greases usually have a lower viscosity and smaller percentage of high molecular Weight components than is desirable to protect bearing surfaces at extremely high temperatures. Therefore, the development of a grease prepared from a base fluid which has a relatively high viscosity and yet 3,712,864 Patented Jan. 23, 1973 possesses excellent low temperature properties would be very desirable.

It has now been found that improved grease compositrons can be prepared by using as the oleaginous base vehicle a hydrogenated high-naphthenic content oligomerized alpha-olefin lubricating oil. Grease compositions prepared from this unique synthetic hydrocarbon oil have been found to possess outstanding lubricating properties over a wide range of temperatures. In addition to being extremely stable, it has been found that the present compositions can be thickened to proper consistency with less gelling agent than was heretofore necessary with synthetic hydrocarbon lubricating oils.

The exceptional properties of the present grease compositions are attributable to the unique synthetic hydrocarbon oil base vehicle employed therein. This synthetic oil comprises hydrogenated alpha-olefin oligomers having from about 12 to 84 carbons per molecule, i.e., generally dimers, trimers, tetramers, pentamers, hexamers and heptamers of C normal alpha-olefins. Unlike conventional olefin polymers, however, the synthetic fluid employed in the present compositions has a high percentage of cyclic oligomers which have been found to have a very pronounced effect on the properties of the finished grease compositions as hereinafter discussed. These cyclic oligomers consist essentially of S and 6 membered naphthenes substituted with several alkyl side chains. Most of the naphthenic oligomers contain a single naphthenic ring although a small amount, e.g., from 0.1 to 0.2 mole per mole of total naphthenic oligomers, contain two naphthenic rings. In general, the synthetic hydrocarbon oil used in the present compositions contains at least 0.7 mole of naphthenic oligomers per mole of isoparaffinic oligomers.

Preferably, the molar ratio of naphthenic oligomers to isoparaflinic oligomers is at least 08:1, and most preferably from 0.85:1 to 1:1. The average molecular Weight of the synthetic base oil is usually about 350 to 700, but more normally from about 450 to 600.

The synthetic base fluid employed in the present compositions has a relatively high viscosity, e.g., a kinomatic viscosity from about 40 to 100 cs., preferably from 45 to 60 cs. at 100 E, which is believed to account in part for the outstanding high temperature properties of the finished grease. Surprisingly, the relatively high viscosity of the base vehicle has been found not to adversely affect the low temperature properties of the grease as would be expected. In fact, the present greases have performed very satisfactorily at temperatures as low as F. This is quite remarkable considering that naphthenic oils in general are classified as low viscosity-index oils and would not be expected to exhibit good lubricating prop erties over such a broad range of temperatures.

The afore-described high-naphthenic content synthetic hydrocarbon oils can be prepared by oligomerizing C normal alipha-olefins under such conditions that a high molar percentage of naphthenic oligomers are produced. The C -C alpha-olefin reactant can comprise either single alpha-olefins or mixtures thereof. Generally, synthetic base vehicles of superior properties are obtained with C alpha-olefins or with mixtures of alpha-olefins having an average chain length of about 8-10 carbon atoms.

An example of a method suitable for preparing synthetic hydrocarbon oils having a high naphthenic content is the method described in copending US. application Ser. No. 47,133 filed June 17, 1970 now Pat. No. 3,682,823. This method essentially comprises contacting C alphaolefin reactant in a liquid phase with an alkali metal tetrahaloalanate catalyst for /2 to 2-0 hours in a reaction solvent or diluent in an inert reaction environment at a temperature of from about 50 C. to 200 C. and a pressure of 1 to 50 atmospheres. The alkali metal tetrahaloalanate catalysts suitable for use in the aforementioned process include those having the general formula MAIX, wherein M is an alkali metal of atomic number from 3 to 55, and X is a halogen of atomic number 9 to 53. Suitable diluents include alkanes, cycloalkanes, and halogenerated alkanes. Particularly suitable diluents are C -C alkanes. Molar ratios of catalyst to alpha-olefin reactant should be on the order of 1:5 to 1:500, with molar ratios of 1:15 to 1:50 being particularly suitable. Preferred reaction conditions include a temperature of from 100 C. to 150 C., a reaction pressure of from 1 to 50 atmospheres and a contact time of between 1 and 4 hours.

It is generally desirable that the oligomerized product be subjected to hydrogenation to remove any residual unsaturation which may be present, thereby improving the stability of final grease product. This can be accomplished by the use of conventional hydrogenation catalysts, e.g., platinum, pallidium or nickel catalysts, at temperatures of from 50 C. to 200 C. and hydrogen pressures at 10 to 2000 atmospheres. Preferred hydrogenation catalysts are nickel catalysts, especially commercial Raney nickel and nickel on kieselguhr.

It may also be desirable to fractionate the oligomeric product to obtain a synthetic base vehicle having a viscosity particularly suited to the application for which the grease will be used.

In preparing the improved grease compositions of the invention, the high-naphthenic content synthetic hydrocarbon oil is gelled to grease consistency by the incorporation therein of a minor amount, e.g., from 1 to 35% w. preferably from 3 to w., of a grease-thickening agent. A wide variety of thickening agents can be employed for this purpose, including conventional soap-base thickening agents, organic thickening agents, or clay thickening agents. Suitable soap-based thickeners include any metal soap of a fatty acid or other fatty material which is capable of providing a stable gel structure to oleaginous base fiuids. The term soap-base is intended to cover conventional metal soaps, complex soaps, and mixed-base soaps. An example of a very suitable soap-base thickener is lithium hydroxy stearate. Suitable organic thickening agents include polyureas, polyamides, amidoureas and the like.

The preferred thickening agents for use in the present compositions are hydrophobic clays. Such thickening agents can be prepared from clays which are initially hydrophilic in character, but which have been converted into a hydrophobic condition by treatment with a hydrophobic surface active agent. Clays having a base exchange capacity of at least milliequivalents per 100 grams are very suitable for conversion into the desired thickening agents, particularly montmorillonites such as bentonite, hectorite and saponite. Other clays such as sepiolite, biotite, attapulgite, illite, vermiculite, zeolite and the like are also suitable. Of the foregoing, bentonite and hectorite clays are preferred, particularly hectorite.

The surface active agents used to convert the clays to a hydrophobic condition can be either cationic, anionic or non-ionic, but preferably are cationic in character and can be either adsorbed on the surfaces of or reacted with the clay. Such hydrophobic surface active agents are well known in the art and are described, for example, in US. Pats. 2,554,222 and 2,623,853 issued to Stross, US. 2,623,852 issued to Peterson, and in U.S. 2,531,440 issued to Jordan. A class of surface active agents which produce particularly effective hydrophobic clays are the amino amides of polyalkylene polyamines formed by reacting polyalkylene polyamines with fatty acids as described in US. 3,050,463 issued to Peterson.

The inherently good oxidation stability and lubricating p p e 9 h p e e t e s qe p ie s m y be arther enhanced by the incorporation therein of oxidation inhibitors such as diphenylarnine, phenyl-alpha-naphthylamine, phenyl-beta-naphthylamine, phenothiazine, hinered phenols, and various alkylated derivatives thereof; corrosion inhibitors such as sodium nitrite and various aminoand benzo-triazoles; extreme pressure agents such as molybdenum disulfides; viscosity index improvers and any other additive or additives known to the art to perform a particular function or functions.

The present composition and the advantages thereof will be further described by means of the examples set forth in Table I and the data presented in Table II. These examples are given for illustrative purposes only, therefore, the invention in its broader aspects should not be limited thereto. Additives have been incorporated into several of the compositions shown in order that realistic comparisons could be made with a commercially available poly-olefin based grease which contains a comparable additive package.

The procedure employed to prepare the clay-thickened greases shown in Table I (Examples 1, 2 and 3) comprised dispersing the bentonitic clay in water which was then acidified with phosphoric acid followed by the addition of the amino-amide hydrophobing agent and the synthetic hydrocarbon fluid. The resulting mixture of clay, surfactant and oil was separated from the water and dehydrated by heating the grease-forming components to a temperature of about 270 F. After the addition of additives and cooling, the dehydrated pre-grease was milled to grease consistency in a 3-roll mill.

The soap-base grease (Example 4) was prepared by mixing 7 grams of oleic acid and 1 gram of sodium hydroxide dissolved in 1 gram of water with 52 grams of the synthetic hydrocarbon fluid. The resulting mixture was stirred and heated to a temperature of 380 F. After cooling and further stirring a No. 2 NGLI Grade grease was obtained having an ASTM worked penetration (60 cycles) of 270.

TABLE I Grease/Example Number 1 2 3 4 Base vehicle:

Fluid A, wt. percent Fluid B3 wt. percent Fluid 0, wt. percent 88 Properties of fluids:

visc. at F., cs. (ASTM D 52. 2 59. 8 51. 2 51. 2 Pour point, D. (ASTM 9757) 65 -70 70 70 Evap. loss at 350 F., wt. percent (ASTM D 972) 10. 1 8. 9 7. 5 7. 5 Thickener:

Hydrophobic clay, wt. percent. 6. 42 6. 30 6. Sodium Oleate, wt. percent 12.00 Additives:

Arylamine-typo oxidation inhlbitors, wt. percent 3. 58 3. 40 3. 58 Thio-diester-type oxidation inhibitor 0. 64 0. 60 0. e4. Anti-corrosion agents, wt. percent. 1.08 1. 03 1.08

l Fluid A-Synthetie hydrocarbon oil having a naphthenic/isoparaflinic molar ratio of 1.00:1, prepared by oligomerizing a mixture of 25% mol l-hexene, 25% mole l-octene and 50% mole l-decene with LiAlCli catalyst in acetalyst/olefin molar ratio of 1/20 at 150 C. for 1% hours. The oligomegrilc product was hydrogenated using a commercial Raney nickel ca a ys 2 Fluid l 3-Synthetlc hydrocarbon oil having a naphthenic/isoparatfinic molar ratio of 0.89:1, prepared by oligomerizing a mixture of 20% mole l-octene and 8075 l-dccene with LiAlOli catalyst in a catalyst/olefin molar ratio of 1 30 at C. for 4 hours. The oligomeric product was hydrogenated using a commercial Raney nickel catalyst.

3 Fluid )-Syntlietic hydrocarbon oil having a naphthenic/isoparatfinic molar ratio of 0.96:1, prepared from the same feed and under similar conditions as Fluid A.

Heetorite clay surfacecoated with an amino-amide hydrophoblng ifagtetnt foiglmed by reacting a mixture of polyethylene polyamines with a yaci s.

In order to demonstrate the excellent properties of the present compositions, Greases l and 3 of the invention were compared with a commercially available olefin polymer-based grease by means of the tests indicated in Table II. The base vehicle employed in the commercial grease is a l-decene polymerization product having a kinomatic viscosity at 100 F. of about 31.7, and a naphthenic/ isoparaflinic molar ratio of about 032:1,

TABLE 11 Grease Number 1 3 X High temperature bearing performance,

10,000 r.p.m. 350 F., hours to failure-.- 643, 660 758, 769 240, 260 Federal Std. Test Method 333 713 991, 423 Even, 22 hrs., 350 F., wt percent loss (ASTM D-972) 3. 5, 2. 7 4. 2, 4. 0 10. 7 Ltfir lgsemp. torque -65 F. (ASTM D Starting, gm. cm 2, 890 2, 770 s, 741 Running, gm. em 7 784 Lgiivemp. torque, -80 F. (ASTM D- Starting, gm. em 7, 139 s, 575 10, 557 Running, gm. em 1, 888 1, 982 1, 152 Lubrication Friction Wear (LFW) Test:

yoles 65, 120 82, 242 Cycles 68, 580 ,352

The e uipment and procedure employed to conduct this test are described the pamphlet entitled A pha Model LFW-l Friction and Wear Testing Machine, published in 1966 by the Dow Corning Corp., Stanford, Conn. The test is designed to evaluate anti-friction and antiwear characteristics of lubricant products. While no specification limits have been established for greases oi the present type, values of over 40,000 cycles are considered excellent, while values of above 60,000 cycles are considered exceptional.

From the data presented in Table II it is evident that Greases 1 and 3 of the invention possess outstanding lubricating properties over a very broad range of temperatures. It is noteworthy that although the fluids used in preparing Greases 1 and 3 have considerably higher viscosities than the fluid employed in Grease X, the low temperature starting torque values of the inventive greases are considerably lower to those of the conventional prodnot.

The excellent stability of the present compositions, as reflected by their low evaporativc loss rates, is attributed in part to the unusually strong afiinity of the base vehicle employed therein for the thickening agent. Because of this afiinity, it was also found that generally a smaller amount of thickening agent was required to gel the high-naphthenic content oils employed in the present compositions to grease consistency, than was required to thicken conventional olefin-polymer fluids. For example, it was found that While it required approximately 4.6% w. of clay to gel a conventional l-decene polymer to an ASTM penetration of 275, it took only 3.8% of the same clay to gel Fluid A to an equivalent penetration.

We claim as our invention:

1. A grease composition consisting essentially of a thickened high-naphthenic content synthetic hydrocarbon lubricating oil comprising hydrogenated C to C oligomers of a C -C normal alpha-olefin, said synthetic hydrocarbon oil having a kinematic viscosity of from about to 100 es. and a molar ratio of naphthenic oligomers to isoparaifinic oligomers of at least 0.7:1.

2. The grease composition of claim 1 wherein the alphaolefin is a C alpha-olefin or a mixture of alpha-olefins with an average chain length of 8. to 10 carbon atoms.

3. The grease composition of claim 1 wherein the oil is thickened with from 1 to 35% by weight of a hydrophobic clay.

4. The grease composition of claim 3 wherein the alphaolefin is a mixture of 25 mole l-hexene, 25% mole 1- octene and mole l-decene.

5. The composition of claim 4 wherein the molar ratio of naphthenic oligomers to isoparailinic oligomers is from about 0.85:1 to 1:1.

References Cited UNITED STATES PATENTS 3,514,401 5/1970 Armstrong et a1. 252-28 3,349,034 10/ 1967 Butcosk et al. 252-28 DANIEL E. WYMAN,'Primary Examiner I. VAUGHN, Assistant Examiner US. Cl. X.R. 25259 

